1. Field of the Invention
The invention relates generally to lensed fluorescent troffer lighting fixtures and particularly to a fixture housing having a reduced profile to allow installation within the reduced volume of shallow plenums commonly encountered in ceiling structures, the housing further being capable of rapid manufacture due to the secure fitting together of components of the housing without the need for separate fasteners.
2. Description of the Prior Art
Lensed fluorescent lighting fixtures are commonly employed in commercial, institutional and industrial applications due primarily to the energy efficiency of fluorescent fixtures generally coupled with relatively low fixture cost even in specification premium installations. Fluorescent lighting in the form of lensed fluorescent troffer lighting fixtures provides acceptable lighting solutions in office environments as well as in other task lighting applications. In such applications as in a commercial office building, literally thousands of fluorescent troffer lighting fixtures are mounted by suspended ceiling grid arrangements and provide desirable lighting performance and pleasing appearance. Lensed fluorescent troffer lighting fixtures can also be surface mounted while providing similar performance. In recessed applications, however, the space within which lighting fixtures are to be mounted has become increasingly smaller, these applications typically being referred to as reduced plenum installations, it being necessary to provide a fluorescent troffer lighting fixture of reduced volume and particularly of reduced depth to allow ready mounting within reduced plenums and yet retain desirable performance characteristics such as minimal lamp image with desirable light outputs. Within this context, the need has further increased in the industry to provide fixtures which can be manufactured at minimum cost yet exhibit exceptionally high performance. Such fixtures must be capable of manufacture with low material cost, low labor cost and must be shipped to a job site with maximum volumetric shipping efficiency. Once at a job site, such low-cost, high performance fixtures must be capable of rapid installation and also provide ever-increasing energy efficiencies while producing desired illumination levels. Lensed fluorescent troffer lighting fixtures must therefore provide a marriage of aesthetic and performance considerations at minimum manufacturing and shipping costs. Grid-type lensed fluorescent troffer lighting fixtures in the present marketplace must be as shallow as possible while still enabling lamping of the fixture while using a minimum of material and retaining the capability of being mounted within conventional grid arrangements including plenums of reduced volume and height. Specification premium lensed fluorescent troffer lighting fixtures such as are produced according to the present invention typically have a greater depth in order to retain desirable lamp image characteristics and are further provided with reflective internal structure capable of preventing light from being trapped behind lamping, thereby to provide maximum illumination efficiencies. In the several embodiments of the invention, deficiencies of the prior art are eliminated in part by use of fluorescent lamping having smaller diameter tubular elements, such as T8 lamping, and relatively low profile electronic ballasts rather than more bulky conventional magnetic ballasts. Economies in manufacture occur according to the present invention through the use of smaller components to form smaller lighting fixtures which retain dimensions necessary for mounting to conventional suspended ceiling grid arrangements, etc. Still further, the structure of those components forming fixture body assemblies as an example is configured to avoid the use of separate fastening elements in the manufacture of such assemblies. Structural portions of present fixture body assemblies are provided with integral fastening elements which allow snap-fit assembly without the need for screws or the like which must be procured separately and separately brought to the assembly location. Fasteners such as screws and the like are also difficult to work with in assembly situations due to small size and the usual necessity for manual placement and manipulation of the fastener. In such situations, a tool is ordinarily required to secure the fastener to the structural elements of the fixture which must be joined together quickly and with precision.
An example of a lensed fluorescent troffer lighting fixture is seen in U.S. Pat. No. 3,045,577 to Lazerson. The Lazerson structure requires use of separate fasteners which limit production in an assembly line environment. The Lazerson structure is also not shaped to allow rapid and efficient mounting in reduced plenum environments and for maximization of fixture stacking once packaged which leads to maximizing of the number of fixtures which can be shipped in conventional transport vehicles. Lewin, in U.S. Pat. No. 3,988,609, describes a lensed troffer lighting fixture intended to be improved by greater efficiencies in a lighting panel or prismatic lens cover provided for the fixture, the fixture itself not being improved relative to the prior art.
Bell et al, in U.S. Pat. No. 5,823,663, describe a fluorescent troffer lighting fixture and particularly a parabolic troffer formed of a housing assembly capable of snap-fit assembly. Kaiser et al, in U.S. Pat. No. 5,806,972, describe a light trap and louver mounting arrangement useful with the housing assembly disclosed in the Bell et al patent. The parabolic troffers disclosed by Bell et al and Kaiser et al relate to the present lensed fluorescent troffers only in the similar concept of providing structure capable of snap-fit assembly without the need for separate fasteners, the particular structures of the present lensed troffers differing from corresponding structures as disclosed in the Kaiser et al and Bell et al patents.
The invention thus provides a lensed fluorescent troffer lighting fixture and particularly a lighting fixture housing assembly wherein the housing assembly is capable of snap-fit assembly of structural body elements without the need for separate fasteners. The structural body elements of the invention which form the housing assembly are provided with fastening elements which are integral with the body elements, thereby yielding savings in material costs as well as in assembly costs while providing a fixture housing assembly having excellent mechanical performance and which contributes to overall fixture lighting performance. The housing assembly of the present lensed troffer lighting fixture further enables production of a fixture having minimum depth to allow installation in reduced plenum environments while retaining desirable performance characteristics including reduction of lamp image and production of desired illumination levels. These performance characteristics are obtained even though preferred lamping for the present fixtures comprises T8 fluorescent lamps which have smaller diameters than commonly employed T12 lamping. The advantages of the invention occur with the retention of traditional and necessary functions such as efficient mounting of a door frame carrying a prismatic lens cover and the like.